## How We Digitally Stretch Our Gallery Wrap Edges Before Printing

As we discussed on the Services page of our website, we digitally “stretch” our image before wrapping it around the edge of our gallery-wrapped canvas images. Here’s how we do that:

Our gallery wraps are either 3/4” thick or 11/2“. On the thin ones, I usually take the 1/4” strip along the edges and stretch it to 1″, thus having an extra 1/4” to wrap around to the back side to cover for variations in the printing and stretching processes. On the larger ones, I take 1/2” and stretch it to 2″ (thus leaving 1/2” on the back). I wouldn’t stretch the image more than four times its original size, but you could go less. To do that, you would effectively be taking a wider margin to wrap around the side.

As an example, if I want a 12” x 18” image stretched around a 11/2” frame, I would crop the image to 13” x 19”. Then, after putting guides 1/2” in from each edge and another guide right on each edge, I would increase the canvas size 3” in both dimensions to get 16” x 22” with the image centered.

1. Click Image ⇨ Canvas Size…
2. Put a check in the Relative Box
3. Make Width and Height 3 Inches
4. Make sure Anchor dot is in center of the grid
5. Hit OK

I would then use a scale transform to digitally stretch the outermost 1/2” to 2” wide, filling the canvas.

1. Make sure Snap is checked in the View Menu
2. Use Rectangular Marquee tool to select the 1/2” strip between the guides along one of the edges
3. Click Edit ⇨ Transform ⇨ Scale
4. Place the mouse cursor over the little square in the middle of the outer edge of the selected area and drag to the edge of the canvas
5. Hit the check mark to finish the transform
6. Repeat Steps 2 through 5 with the 1/2” strips along the other three edges

(Actually, I first do the four corner squares separately, but since only a small bit along the edge of those squares has any chance of being seen, you could include them in either the horizontal or vertical strips (or even both)).

Then I add a blank (transparent) edge around the image representing the canvas I need for stretching the canvas around the frame by increasing the canvas size by double the required margins in both dimensions, the same way we did above. That margin would be at least the width of the moulding along the bottom (1″ for the 11/2” moulding we are using now) and enough extra to get a grip with the canvas pliers (for me that’s at least 3/4“). That would make the image’s final dimensions at least 191/2” x 251/2“. When I am finished, I add layers with cut lines, fold lines, staple lines, positioning marks for the hanging hardware, etcetera, but that is a personal matter beyond the scope of this article.

## A Solution To Second Mat(h) Problem

Sadly, we had no winners to this contest. Here is a solution to that math problem:

There is more than one way to solve this problem, but we will be exploiting three different relationships. First, in preserving the aspect ratio, the length of the image (we’ll call L) is 11/2 times the width (W). $L = 1.5W$. Then, adding up the components making up the overall width of the mat, the image width (less two overlaps of 1/8“) plus two mat widths (M) would equal 16 inches. $W - \frac{1}{4}" + 2M = 16"$ By the same token, the image length (less same overlaps) plus two mat widths would be 20 inches. $L - \frac{1}{4}" + 2M = 20"$

If you replace the L in the last equation with its W equivalent from the first equation, and then add 1/4” to both sides of both equations to combine constants, you are left with the following two equations to solve with two unknown variables:

$\begin{array}{r c l} 1.5W & + 2M = & 20.25 \\ W & + 2M = & 16.25 \end{array}$

From here you can use linear algebra (matrices) or algebraic manipulation to simplify until you are left with just one variable. For example, just subtracting the bottom equation from the top (subtracting the left sides separately from the right sides of each equation), you will wind up with

$0.5W = 4$

which means the image width is eight inches, which means its length is twelve inches, and the mat guide would be set to 41/8“.

### What’s Next

I’ve come up with one more printing-inspired math problem, which I will share as soon as I master a new plug-in for this blog.  After that, I’m not sure.  Response has been weak, but the former teacher in me feels a need to keep pointing out opportunities to use some of this stuff you learned in school (or is it just to torment those students who were the most difficult – I’m not telling).  This isn’t really costing anything, and I give enough warning for the math-averse to stay clear.  Stay tuned.

## Plans For Making A Cardboard Box For Framed Art

I just added an article to the website (Making A Cardboard Box To Ship Art) that has plans and instructions for making a cardboard box. To make any size box, all you have to do is plug your dimensions into the expressions for each measurement on the plans. You can even download and print the plans (but not the instructions – hmmm).

As per my last post, you can also reach this article from “Tips & Techniques” on the main menu. Click on “Printing & Beyond”, which will take you to the “Do-It-Yourself Ideas For Finishing Your Photographs“. The sitemap will also work.

Enjoy!

P.S.  I’ve promised to publish plans and instructions for making our booth display panels in a form that people can actually use, instead of just the notes and scribbles I made for myself at the time, but those won’t be ready for the beginning of the next Florida art festival season as I had hoped.  The cost of materials for one three-foot wide panel was about $50 a few years back. Stay tuned. ## More About Adjusting A Logan Sander It occurred to me the other day that it might be good to be able to download the steps to adjust a Logan Sander, as I described in Another Method For Adjusting A Logan Precision Sander. While converting to the Acrobat .pdf format, I took the liberty of adding more information and, I hope, making it easier to follow. To download, click on the link below. Enjoy! Get printable version(.pdf) ## Another Method For Adjusting A Logan Precision Sander We have a Logan Precision Sander Elite Model F200-2 disk sander for improving saw-cut miters for your picture frames to a “perfect 45°” after cutting the moulding to size on our miter saw. To maintain such perfection requires due diligence and occasional adjustment. ### How Do You Know When It’s Time To Adjust Your Sander? 1. You may notice that when you put your frames together, there is a small gap between the pieces of moulding either on the inside of all four corners or the outside of all four corner. If some corners have gaps on the inside and some have a gap on the outside, you have other problems. In the figures used in this article, the symptoms have been exaggerated for illustration purposes. If the condition of your sander gets this bad without you noticing, you may want to consider another profession or hobby. 1. When you are comparing the lengths of opposite pieces, and you have them side by side with the miters face up and their back sides touching, you may notice by running your finger over the miter that they are the same length on one end of the miter but not the other, or that one piece of moulding is higher at one end of the miter and the other piece is higher at the other end. In either of these cases, it’s time to adjust your sander. ### But What About The Miter Saw? It may be true that the miter saw also needs adjustment, but that would have minimal impact on your frames, because even if the angle of the cut was wrong, the sander should correct that problem. Of course it would take more sanding to correct, which beside taking more time and effort could, in the worst case, result in your frame being too small, so it should periodically be checked and corrected according to the manufacturer’s instructions (I currently have no improvements or suggestions for that process). An indication that the miter saw needed adjustment would be if as you are sanding the miter, sawdust builds up on top of one side of the moulding faster than it accumulates on the other. If it takes too many revolutions of the sander to perfect the edge, that could also be a clue, or it could be time to change the sandpaper. ### How To Adjust The Sander On the last page of the 4-page manual (available at www.logangraphic.com) are simple instructions for that adjustment that should work well if you are willing to follow Step 1 and remove the sandpaper. To see the Note click here.To hide the Note click here. The full instructions are as follows: Adjustment 45° 1. Remove sand paper 2. Place the 45˚ square flat against the wheel and up against bar (Fig. 7). Look for gaps against the bar. 3. Adjust the bar using adjustment wrench until gap disappears. When I don’t remove the sandpaper disk the technique doesn’t work as well, so I’ve come up with an alternate set of instructions: 1. Put miter cuts on both ends of two long scrap pieces of your widest moulding. 2. When you sand a piece of moulding, each end will use a different side of the sander. Call one side of the sander “A” and the other “B”. As you sand the two pieces of moulding, mark the back of each end of each piece with the side of the sander used (A or B). 3. Find a good right angle, either in a reliable carpenter’s square or using other methods. 4. Flip one of the pieces of scrap moulding upside down so you can join Corner “A” on both pieces to make a 90˚ (right) angle. Flipping is very important*. 5. Put one piece of moulding along one edge of the reference angle (carpenter’s square) and slide the reference toward the second moulding until it just touches at one end or the other (if it touches at both ends, you are finished with Side A – skip ahead to Step 7). Measure the error gap (I like millimeters only because they are so small) at the end of the moulding that’s away from the reference line. Then measure the length of that piece of scrap moulding (using the same units of measurement). 6. The adjustment screw on my sander had 32 threads per inch, and it was 109 millimeters from the pivot point. Based on that, your multiplier will be 25,000. To see the Note click here.To hide the Note click here. I’ll do the math just in case your sander has different measurements so that you can substitute the real numbers in for mine at the proper places. One complete turn of the adjustment screw is 360° or 1/32” and there are 25.4 millimeters per inch, so the constant multiplier would be 109 mm * 360° per turn of screw * 32 threads per inch ÷ 25.4 mm per inch ÷ 2 errors = 24,718.11. We’ll say 25,000. Divide the error you measured in the last step by the length of the moulding that you measured and multiply by 25,000. Your result will be the number of degrees you need to turn the adjustment screw. If the error gap was at the corner, then the angle is too large and you have to turn the screw counterclockwise to back it out. Conversely, if the error gap was at the end of the moulding, then the angle is too small and you have to turn the adjustment screw clockwise to push it out more. After making the adjustment, you may want to retest by repeating the process by starting at Step 2 and resanding the same two corners just used. Before sanding, I recommend drawing a line all the way across the end of the moulding with a pen or marker and then sanding until the line completely disappears. 7. Repeat this whole process (starting at Step 4) for the other two miters, labeled “B”. Remember, for these two you will be playing with the adjustment screw on the other side of the sander. That’s all there is to it. Congratulations. To see the Note click here.To hide the Note click here. #### Math Warning: a quick note about trigonometry (OPTIONAL)! This process was concerned with angles, not distances, but since angles are harder to measure with any precision we had to convert. When you take the ratio of the two perpendicular sides (the sides that are 90° apart) of a right triangle containing the angle you are interested in, that’s called the tangent of that angle, and you can have a good calculator app on your phone find it for you (for my Droid, I found RealCalc Plus by Quartic Software at the Play Store and was happy to pay$3.50. There are plenty of other options, though).

The error angle you measured (indirectly) was actually twice as large as the real error. One problem is that the tangent curve is not generally a straight line, which means that the tangent of twice some angle is not the same as twice the tangent of that angle. That’s why the normal procedure would be to convert to angles, do the adding, subtracting, or multiplying, and then convert back to distances we can measure again. We were able to use the small angle exception, however. It turns out that for angles less than say 10°, the tangent curve IS pretty straight and the error introduced by taking our shortcut isn’t worth worrying about. That’s what we did, and that’s why the problem was so easy. That’s your math lesson of the day week month. Let’s get back to work.